> i.e. i could catch devices/drivers attachment and detachment. By device
> identifucation info you can find your expected device and upper level
> driver, uhid in your case.

I'll try that but I fear that I'll get uhidev* as the upper level
driver. uhidev itself doesn't seem to be useful here because it's
only a dispatcher which hands the data to the uhid devices.
So if I have 2 USB HID devices each having 2 report IDs, I'll
probably have something like:

      uhidev0 (vendor A, product B) ->  repID 0xAA -> uhid0
                                    ->  repID 0xBB -> uhid1
      uhidev1 (vendor C, product D) ->  repID 0x56 -> uhid2
                                    ->  repID 0x77 -> uhid3

So I think I can get from usb(4) which vendor/product is on
uhidev0. I also can get from uhid0 the report ID it gets it's
data from (e.g. repID 0xAA). But I cannot query uhidev0 for
it's attached uhid devices nor can I query uhid0 for it's lower
layer uhidev device. There seems to be a missing link?

Werner